POLYMER-SOLVENT DIFFUSION AND EQUILIBRIUM PARAMETERS BY INVERSE GAS-LIQUID-CHROMATOGRAPHY

The solubility and diffusion coefficients of low-molecular- weight penetrants in a polymeric stationary phase were determined by use of inverse gas chromatography (IGC). Previously reported applications of packed-column IGC to the measurement of the stationary-phase diffusion coefficient have been carried out via the van Deemter approach. We present here a new mathematical model to describe the chromatographic process in packed columns. A moment analysis procedure was developed from this model to analyze the chromatographic peaks eluting from packed columns. The first moment (mean retention time) is determined to depend only on the equilibrium partition coefficient, whereas the second moment (variance) is related to both the thermodynamic and transport properties of the polymer-solute system. The validity of the technique was demonstrated by measuring the diffusivity and solubility of toluene and benzene in polystyrene above the glass transition temperature of the polymer. Free-volume theory was used to interpret and correlate the diffusivity data obtained at infinite dilution of the solute. One can use the results obtained at infinite dilution to predict reliably via the free-volume theory the concentration and temperature dependence of polymer-solvent diffusion coefficients.